(a) Field of the Invention
The present invention relates to a cathode ray tube, and more particularly, to a cathode ray tube having a support member that enables mounting of a color selection apparatus to an inner area of a panel in which a phosphor screen is formed.
(b) Description of the Related Art
A cathode ray tube (CRT) is typically a display device in which three electron beams emitted from an electron gun strike R, G, and B phosphors of a phosphor screen to illuminate the phosphors and realize predetermined images. The CRT includes a panel having the phosphor screen, a neck in which the electron gun that emits electron beams toward the phosphor screen is mounted, and a funnel that interconnects the panel and neck. A deflection apparatus for deflecting the electron beams is mounted to an outer circumference of the funnel.
In such a CRT, the color selection apparatus is mounted to an inner area of the panel. The color selection apparatus performs a color separation function such that the electron beams emitted from the electron gun are separated to land on desired phosphors. The color selection apparatus includes a shadow mask that separates the electron beams, a mask frame for supporting the shadow mask, and a support member that secures the mask frame to the inner area of the panel.
The shadow mask of the color selection apparatus is formed by performing a photolithography process on aluminum-killed steel or Invar steel of an extremely small thickness to form a plurality of electron beam passage apertures, after which drawing is performed to realize the final desired form. Since the thickness of the shadow mask is extremely small relative to its area, and because of the formation of tens of thousands of the apertures, the shadow mask becomes structurally weak. This leads to the shadow mask sinking inwardly after receiving an outside shock, or undergoing thermal expansion (i.e., doming phenomenon) toward the phosphor screen as a result of the electron beams that do not pass through the apertures and instead strike the shadow mask.
To overcome this problem and also enable manufacturing of larger screen sizes and flatter profiles, tension masks have been developed that are fixed to a frame of a predetermined structure while in a state of tension. An example of a CRT that uses a tension mask is disclosed in U.S. Pat. No. 6,271,624.
However, in the CRT using the tension mask, doming as with the conventional shadow mask nevertheless occurs, which causes mislanding of electron beams. This is a result of the tension mask being heated by the electron beams that do not pass through electron beam apertures and strike the tension mask. That is, the heat generated in the tension mask is transmitted to the frame that supports the mask such that the frame undergoes thermal expansion.
To prevent this problem, the CRT having the tension mask uses support members for securing the frame that mounts the tension mask to the panel. Each of the support members includes a spring holder (or hook), one end of which is welded to the frame; and a spring having one end welded to the spring holder and its other end fastened to the spring holder mounted to an inner surface of the panel. Each of the spring holders is formed of a bi-metal member, in which a high expansion member and a low expansion member having different thermal expansion coefficients are connected aligned in a lengthwise direction.
With the support member having such a structure, the spring holders are thermally deformed by the bi-metal characteristics when the frame undergoes thermal expansion. Therefore, movement of the frame caused by its thermal expansion is compensated for by the spring holders to ensure that the tension mask remains at its intended, original position. This prevents mislanding of the electron beams by thermal expansion of the frame. However, the bi-metal members forming the spring holders are high in cost and difficult to work with during manufacturing. This increases overall manufacturing costs of the CRT.
In Japanese Laid-Open Patent No. Heisei 9-231913, a CRT that does not use costly bi-metal parts and that has plate-shaped support members for preventing the mislanding of electron beams is disclosed. In this disclosure, the support members include welding sections that are welded to the color separation apparatus, locking sections suspended from and connected to the panel on which the phosphor screen is formed, and center sections interconnecting the welding sections and the locking sections. The welding sections, locking sections, and center sections are partitioned by a pair of folding traces, which are provided in parallel and at a predetermined angle with a direction along a width of the support member.
If the frame undergoes thermal expansion, the deformation of the support members structured in this manner follows the thermal expansion of the frame. This therefore compensates for position changes that would cause mislanding.
However, with such support members, an area of the welding sections, which are supported by hooks and fixed together with the hooks on the color separation apparatus, occupies a significant portion of the entire area of the support members. As a result, the welding sections limit the range of operation of other areas when the support members are operating. This reduces the effectiveness of operation of the support members.
To overcome this problem, Japanese Laid-Open Patent No. Heisei 11-219664 discloses a structure in which, while using the above conventional structure of the support member, two folding traces for compensating for a slant of a plane surface of the locking sections, which oppose the plane surface of the welding sections, are formed in the locking sections.
However, in this disclosure, based on folding traces defining the welding sections and center sections according to a plurality of folding traces established on the support member, the support member (excluding the welding sections) moves freely about the remaining folding traces. As a result, the support members do not operate according to design specifications when applied to the CRT.
Further, there are problems in the processes involved as a result of a plurality of folding traces being designed on the support members. That is, since it is necessary to bend the support members repeatedly, manufacturing becomes complicated. Also, when the support members are formed by bending, it is difficult to bend the support members within a range to avoid breaking of the support members and to determine the bending angle when considering the high strength of the material used for the support member.